A motion guide device is mounted in a robot, a machine tool or a semiconductor/liquid crystal manufacturing apparatus and is used to guide linear movement or curvilinear movement of a moving body.
Known as a motion guide device are a linear guide, a ball spline and the like. The linear guide has, as illustrated in FIG. 15, a track rail 31 having ball rolling grooves 31a formed therein, and a moving block 33 mounted on the track rail 31 via a plurality of balls 32 to be slidable along the track rail 31. In the moving block 33, a plurality of loaded ball rolling grooves 32a facing the ball rolling grooves of the track rail 31 and ball return paths 38 in parallel with the loaded ball rolling grooves 32a are formed. To each traveling-directional end of the moving block 33, an end plate 34 is attached. In the end plate 34, a U-shaped direction change path 35 is formed connecting the loaded ball rolling grooves 32a and the ball return paths 38 extending in parallel with each other. These loaded ball rolling groove 32a, ball return path 38 and direction change path 35 constitute a circular ball circulation path.
After rolling in the ball rolling groove 31a of the track rail 31, each ball is scooped up by a scooping portion 37 at the lower end of the end plate 34 and enters the direction change path 35. Then, the ball passes through the ball return path 38 and the opposite-side direction change path 35, and then the ball is pushed by the following ball 32 to enter the ball rolling groove 31a at the scooping portion 37.
In such a motion guide device, when the moving block 33 is moved at high speed, the scooping portion 37 at the lower end of the end plate 34 is sometimes damaged, which is a problem. This damage is caused because when the ball 32 rolls from the direction change path 35 into the ball rolling groove 31a, the ball 32 pushes the scooping portion 37 outward by a centrifugal force or the ball 32 is pushed near the scooping portion 37 toward the outside of the scooping portion 37 by a meandering follow-on ball 32. Besides, when the ball 32 is scooped up from the ball rolling groove 31a, a scooping force is applied to the scooping portion 37.
In order to solve this problem, there has been developed a motion guide device of which a scooping portion is hardly damaged even when the motion guide device is operated at high speed. For example, as shown in FIG. 16, the motion guide device as developed has a scooping portion 37 of which a tip end is cut off and a cut surface 37a is a flat surface perpendicular to the ball rolling groove 31a (see patent document 1). According to the invention disclosed in the patent document 1, as the sharp-pointed tie end of the scooping portion 37 is cur off, it is possible to enhance the strength of the scooping portion 37. However, as the cut surface 37a is the flat surface perpendicular to the ball rolling groove 31a, it is difficult to circulate a ball 32 smoothly.    [Patent Document 1] Japanese Patent Laid-open Publication No. 2004-68880    [Non-Patent Document 1] Japanese Patent Application No. 2004-246524